Antenna structure



Jan. 18, 1955 I JASIK 2,700,112

ANTENNA STRUCTURE Filed March 7, 1949 2 Sheets-Sheet 1 PIEIE' IN V EN TOR. BY [fem "g J m/A lm/ M9 2 Sheets-Sheet 2 H. JASIK ANTENNA STRUCTURE Jan. 18, 1955 Filed March 7, 1949 m N m MM r m M fi e Y B United States Patent ANTENNA STRUCTURE Henry Jasik, Watertown, Mass., assignor to Andrew Alford, Boston, Mass.

Application March 7, 1949, Serial No. 79,969

6 Claims. (Cl. 250-33) The need for a high frequency dipole of a simple design, having substantially unchanging characteristics over a wide frequency band has existed for some time. The chief objection to antennas of this general type is that they are mechanically weak because of the stresses placed on the insulators when the antenna is subjected to rough handling.

The antennas described in my invention have wide band characteristics and have a mechanical design such that the insulators are placed only under compressive stresses. Almost all high frequency insulatingmaterials can withstand considerable compression but are quite weak when subjected to tension. In previous designs 'in-' sulators as used are often subjected to tensile stress, with the result that they are frequently fractured thus rendering the antenna useless.

In my invention two radiating outer sleeves are employed with an insulating spacer separating the sleeves. The end of one of the outer sleeves spaced away from the other end near the insulating collar is at zero potential. A metallic means for spanning the sleeves in their longitudinal direction exerts a compressional stress between opposite faces of the insulating collar.

The structure of the'present invention may be carried out in various forms as for instance, in a completely balanced structure in which a gap exists on either side of the neutral plane or in a unit where the neutral plane is at one end of the structure. The structure may also employ special coupling means connected between 00- axial feed cables and the antenna or other special compensating elements which enter individually and in combination to form the distinguishing features of the present invention.

Without further discussing .the merits and advantages of the present invention which will be more fully learned from the specifications and claims set forth below, the invention in its various embodiments will be described in connection with the drawings forming a part of the specifications in which;

Figure 1 is a longitudinal section taken through one form of the antenna.

Figure 2 shows a substantially equivalent electrical circuit diagram for the structures of Figure l.

Figure 3 shows in longitudinal section a modified form of the structure shown in Figure 1.

Figure 4 shows a substantially equivalent bilineal circuit diagram for the structure of Figure 3.

Figure 5 shows a longitudinal section of a further modification of the structure shown in Figure 1, and

Figure 6 shows a substantially equivalent electrical circuit diagram of the structure shown in Figure 5.

In the embodiment of my invention shown in Fig. 1, 1 and 2 are sleeve radiating elements of metallic material, the lower part of 2 being electrically connected to a ground plate or base 21 by Welding or by other suitable means while the upper sleeve 1 is capped by a-cover 22 which may be of metal. The base 21 may be considered to be at zero potential. The member 3 is an insulating collar which may be made of a'tough plastic material and have a shape to fit snugly against the outer surface of the sleeve ends with a centrally inwardly extending flange filling the space between the end edges of the sleeves separating the two sleeves 1 and 2 by a desired gap distance. The element 4 is a metallic rod which at one end is secured by welding or by other suitable means to the ground plate 21, making electrical connection and at the other end is threaded as at 24 to receive a washer and nut 25 which is tightened against a conductive plate 26 fitting inside the tube 1 and welded to its inner wall just beyond the end resting on the insulator 3 so that the adjacent ends of the tubes 1 and 2 are pressed against opposite faces respectively of the insulator flange putting the insulator under substantial initial compression. The element 5 is a coaxial cable with an inner conductor 6 and an outer conductor 7 which is conductively connected to sleeve 2. The coaxial cable 5 passes through the plate 21 and is connected to the high frequency line by means of the cable connector 20 which may be silver soldered to the plate 21. The inner conductor 6 of cable 5 is connected to rod 4 by the connector 13. Rod 4 is connected to plate 26 and hence a potential is set up across the gap separating sleeves 1 and 2. If desired the plate 26 may be closer to the insulator flange than shown in Figure l, in which case the series inductance 12 (Figure 2) on one side of the coaxial line would be decreased. The potential which is impressed by the connections of the coaxial cable sets up radiating currents on the outer surfaces of sleeves 1 and 2. The coaxial cable 5 with inner conductors 6 and outer conductor 7 apply a voltage to a shunt reactance formed by the reentrant circuit consisting of outer and inner surfaces of tube 18, the lower part of rod 4, the inner surface of plate 21 and of the tube 2. The tube 18 has a metallic plug 14 at its upper end through which the rod 4 is threadedly engaged with a washer 27 end nut 28 to clamp tightly the eyelet and of the conductor 13 and the rod 4 to the top surface of the plug. The effect of this reactance is shown as a shunt 13 across the coaxial cable. This reactance is used to help to compensate the impedance as seen by the coaxial line.

The radiation impedance 10 (Figure 2) of the an-v tenna proper can be changed by varying the diameter and length of sleeves 1 and 2. Two other variables as noted just below are useful for impedance compensation. .The length of the insulating collar 3 is used to control the shunt capacitive reactance across the radiation impedance. A decrease in the gap space will decrease the which is designated as 12 in Figure 2 as has been stated.v

The complete equivalent compensation network as has been stated is shown in Figure 2 the elements of which have already been referred to above. In part recapitulation 10.is the radiation impedance of the sleeves 1 and 2, 11 is the capacitive reactance due to the gap spacing, 12 is the inductive reactance of the upper part of rod 4, and 13 -is the reactance as explained above across the coaxial line.

Another embodiment of my invention is shown in, Figure 3. The same elements used in the modification of Figure 1 will bear the same numerals in all of the other figures where there is no structural change. In Figure 3 the rod 4 extends through the cap 22' and compresses the sleeves 1 and 2 together against the insulator 3 from their extreme ends by tightening the nut on the rod4 on the outside of the cap 22. The internal plate is therefore omitted and the coaxial cable 5 has its internal conductor 6 connected by a short lead 30 to the end of the tube 1 adjacent the gap. The outer conductor 7 is m good electrical contact with the inside of the tube 2 substantially up to the end adjacent the gap.

The equivalent circuit diagram is shown Figure 4. The gap reactance is shunted across the coaxial cable as indicated at 11 with a radiation impedance 10' also in shunt across the coaxial cable. Due to the shortness of the connector 30 there is substantially no series reactance on one side of the line as indicated in Figure 2 but there is a considerable shunt inductive reactance made up of the rod 4, part of the base 21, and part of the upper sleeve 1. The lower section of the rod 4 and base 21 corresponds to a reactance 32 which is substantially equivalent to reactance 13 of Figure 2 while the reactance 31 accounts for the additional upper section of the rod 4'.

The arrangement shown in Figure 5 is a balanced system consisting of a structure which electrically differs somewhat from the structure of the other figures. In Figure 5 the structure on the left is the same as that on the right with a neutral mid-plane.

The device comprises inner sleeves 41, actually a sin- (Figure 2) gle tube and outer sleeves 42 spaced by the insulators 43 which correspond to similar elements described in connection with the other modifications. concentrically positioned and supported within the sleeves and insulators are the feeder tubes 44 within which is positioned the tie rod 45 which extends from one extreme outer sleeve 42 to the other and serve as the means for putting the sleeves and insulators under compression. For this purpose plates 46 are secured inside the sleeves 42 near their outer ends by welding the sleeves to these plates while the rod 45 extends through holes in the center of the plates and on the other side is drawn tightly by a suitable nut 47. Within the sleeves 42 are plates 48 through which the feeders 44 extend which feeders are concentrically positioned with respect to the sleeves. These .plates 48 are .also Welded to the tubes or sleeves 42 and make good .electrical connections both with the inside of the sleeves 42 and the outside of the feeder 44. The position of the plates 48 with respect to the gap has a substantial eifect on the value of the terminal impedance of the concentric feeders consisting of the tubes 44 and 41. An increase in this spacing has the effect of increasing the inductive reactance in series with impedance of the end part of sleeve 42. The two plates 46 and 48 provide strong supports .for the tube 44.

The outer ends of the sleeves 42 may be capped by caps 49 which may be secured in .any desirable way. Insulating discs 50 act as supports for the tie rod 45 and spacers for the tie .rod within the tube 44.

The single tube 41 .has an opening at the top center section closed by a cover plate 51 fitting on a cover plate mounting 52 .so that the device can be reached in the region where the feed lines are brought up to the structure just described.

The means and method of feeding the sleeve antenna is optional and may be accomplished by the application of a balanced feed, compensated as desired, between right and left feeders 44. In Figure 5 there is shown a single coaxial cable 53 with an outer conductor 54 connected by a connector 55 to the feeder 44 and an inner conductor 56 connected by a connector 57 to the other feeder 44. A section of a compensating reactance 58 is also shown connected to the connector 57. The balanced voltage in this case is supplied between the outer conductor 54 and the connector 57 or the tube 58.

The equivalent circuit diagram is shown in Figure 6. The balanced supply voltage is shown at 59. This is applied to a transmission line 60 consisting of the sleeve or tube 44 as the high side and the inner side of the sleeve 41 as the grounded side. Reactance 64 comprises the inside of the tube 44 and the plate 4.6 to the tie rod 45 and the tie rod 45 to the neutral plane. 61 represents a series inductance which includes the plates 48 and the section of the tube 42 from where the plate 48 is connected to it, to the gap. 62 represents the gap shunted across the line and 63 represents the radiation impedance. It will be understood that the circuit is only a half circuit of Figure 5 since the same elements in the same position are repeated for each side.

In all of the circuits shown the system has a neutral or ground plane away from the air gap and this distinguishes this type of antenna from the so called dipole antenna. In the balanced system of the present invention the antenna length may correspond to a half wave length of a frequency chosen .in the band width. In the unbalanced system it may correspond to a quarter of a wave length and is fed in the manner indicated above.

Having now described my invention I claim:

1. An antenna structure having a central plane of symmetry comprising a sleeve having symmetrical aligned sections extending normal to said plane of symmetry on both sides thereof, a set of sleeve sections aligned with said first sleeve extending outward from the ends of said first sleeve, short rigid insulating collars positioned between the ends of said first sleeve and the adjacent opposing ends of the set of sleeve sections, conductive cylinders extending coaxially at each side of said central plane through a part of said first sleeve and one each of said sleeve sections, transverse plate elements rigidly securing said conductive cylinders to said sleeve sections, a metallic tie rod extending through said conductive cylinders and through said central plane, means adjustably anchoring said tie rod to said sleeve sections for clamping the ends of the sleeve sections and the first sleeve on opposite sides of said insulating collar and holding said sleeve sections and said first sleeve in a rigid structure and means for feeding said sleeve sections thifimgh said conductive cylinder across said insulating co ar.

2. A device as set forth in claim 1 in which the tie rod is concentrically positioned within said conductive cylinders.

3. A device as set forth in claim -1 in which said conductive cylinders are conductively connected to said end sleeves near the air gap.

4. An antenna structure comprising a centrally positioned sleeve, end sleeves at both ends of the central sleeve, insulators positioned between the adjacent ends of the end sleeevs and central sleeve, a conductive tie rod extending through said centrally positioned sleeve and into the end sleeves through said insulators, conductive plates filling'the complete cross sectional space of the end sleeves away from the position of the air gap formed across the insulators, said conductive rod being attached to said plates, conductive tubes having ends attached to said conductive plates and concentrically positioned with respect to said sleeves, and means for feeding said structure across the gaps formed by said insulators with a balanced feed in which the central plane transverse to the central sleeve in its mid-section has a neutral potential.

5. An antenna structure comprising a centrally positioned sleeve, end sleeves at both ends of the central sleeve, insulators positioned between the adjacent ends of the end sleeves and central sleeve forming capacitive gaps, conductive .means within said sleeves acting longitudinally to exert pressure on said insulators, and means forming transmission lines within the sleeves for feeding each sleeve section across the gap formed by the insulators, said means comprising coaxial cable sections formed by the inner surface of the sections of the central .sleeve on either side of a mid-plane of the central sleeve as one set of conductors and internally positioned tube sections concentric with said central sleeve as the other :set of conductors.

6. ,An arrangement as in claim 5 including means for feeding the inner ends of said concentric tubes with opposite potential and maintaining the mid-plane of the central tube at a neutral point.

References Cited in the file of this patent UNITED STATES PATENTS 2,201,857 Dome May 21, 1940 2,321,454 Brown. June 8, 1943 2,385,783 Alford Oct. 2, 1945 2,462,865 Himmel Mar. 1, 1949 2,463,547 Meier Mar. 8, 1949 2,471,045 Selvidge May 24, 1949 2,513,157 Ferris et al. June 27, 1950 2,543,085 Willoughby Feb. 27, 1951 FOREIGN PATENTS 446,441 Great Britain Apr. 30, 1936 

